1. Technical Field of the Invention
The present invention relates to a method and device for connection admission control in ATM networks for determining whether calls may be connected by estimating cell loss ratios based on traffic parameters specified by users.
2. Background Art
In ATM networks, a number of service categories are available for responding to traffic having different properties (transmission speed, quality of service, etc.). Therefore, a connection admission control method which assumes the presence of a plurality of service categories is required.
As methods for connection admission control for determining whether calls may be connected based on traffic parameters specified by users, there are techniques wherein specific Quality of Service (QoS) requirements are fulfilled. These QoS requirements, for example, may be determined by cell loss ratios relating to the virtual paths (VPs) containing the calls.
As examples of connection admission control methods which perform processing in real-time, connection admission control methods which can be applied to a single service category (especially those assuming Variable Bit Rate) are commonly known. In these methods, traffic parameters (peak cell rate and sustainable cell rate) reported from users are taken as inputs, and connection admission processing is performed within a standard period of time without depending on the number of calls or the traffic conditions. These methods are applied for each VP, and are carried out in the connection admission control section 1' shown in FIG. 7 by means of the flow procedure shown in FIG. 8. Hereinbelow, this method will be explained in detail.
(1) In order to process call connections in real-time, the parameter N for the number of iterations is predetermined so that a single connection admission procedure is completed in a specific period of time.
(2) For each VP, an identifier i (i=1, 2, . . . , number of already set up connections+1) is provided for every user which has already been assigned a call or for which there has been a new call set-up request in the VP. A user i which issues a new call set-up request reports the peak cell rate r.sub.i (1/sec), the sustainable cell rate a.sub.i (1/sec) and the specified cell loss ratio value to the connection admission control section 1' (see FIG. 7).
(3) The connection admission control section 1' determines the maximum number of cell arrivals R.sub.i and the average number of cell arrivals A.sub.i in a time interval which is a constant .gamma. times the time period required for the VP to transfer a single cell according to the following formulas (step Sf1) based on a peak cell rate and sustainable cell rate reported by the user. ##EQU1##
Here, INT(x) is a function for the minimum integer greater than or equal to x. L represents the cell length (bit/cell). C represents the VP capacity (transmission speed in bit/sec). .gamma. represents a constant (cells) which depends on the output buffer capacity K of the multiplexing device.
(4) The average C.sub.1, variance C.sub.2 and third central moment C.sub.3 of the distribution of the number of cell arrivals for traffic in the case of assuming that a connection has been admitted for a new call set-up request are determined by the following formulas (step Sf2). ##EQU2##
Here, n denotes the number of connections both already set-up and required to be set-up.
(5) If for a pre-determined parameter N denoting the number of iterations, the third central moment C.sub.3 satisfies the following inequality: ##EQU3##
wherein ##EQU4##
then the third central moment C.sub.3 may be redefined, as a corrected value, to the following (step Sf3): ##EQU5##
(6) R and A are determined by the following formulas (step Sf4). ##EQU6##
(7) The estimated cell loss ratio value *B is determined by the following equation (step Sf5). ##EQU7##
In this case, when k=0, 1, 2, . . . , then ##EQU8##
otherwise, EQU *p(kR)=0
The amount of time required for this calculation does not depend on the number of types of calls or the number of calls, and is completely determined by the pre-determined parameter N which is the number of iterations. According to this calculation, a sufficiently precise value for the cell loss ratio estimate *B can be obtained.
(8) The connection admission control section 1' compares the above-mentioned cell loss ratio estimate *B with the specified cell loss ratio reported for the "relevant call" and "all calls already set-up in the VP in which the call is to be set-up". Then, as a result of the comparison, when the above-mentioned cell loss estimate *B is less than any of the specified cell loss values, the call for which connection has been requested is determined to be connectable (step Sf6). If not, the call connection is determined to be impermissible. Then, the results are reported to the users (see FIG. 7).
(9) When connection is determined to be possible in all of the VPs through which the call passes, then the connection of the call is permitted.
According to the above procedure, it is possible to perform connection admission control of a call within a pre-determined time period.
The above-mentioned conventional art does not perform convolution calculations which depend on the number of connections and the number of types of calls. For this reason, the calculation time is determined solely by the pre-determined parameter N denoting the number of iterations and it is possible to determine the cell loss ratio estimates *B based on calculated amounts which do not depend on the VC numbers or VC classification numbers, so as to achieve real-time connection admission control which satisfies the communication QoS requirements determined by the cell loss ratios.
However, in actual practice, connection admission processing must be capable of handling a plurality of service categories, and connection admission control methods responsive to only a single class (such as only VBR) are inadequate. In ATM networks, traffic of different service categories shares the transmission paths, so that the behavior of traffic belonging to on one service category may have an adverse influence on traffic belonging to another service category. Hence, it is not suitable to determine whether or not to allow a call to be connected independently by the service category. Therefore, there has been a demand for a multi-class connection admission control method which determines whether or not to allow a call to be connected while simultaneously predicting the influence on the QoS of a plurality of service categories.